It is important for pharmacy technicians to be familiar with common dosages and dosage forms and strengths. This will make it easier to identify the correct drug, communicate with other healthcare professionals, and even detect potential fake prescriptions. Questions on the PTCB Exam on this topic may include calculations.
Drug strength is the amount of active drug in any given dosage form. The drug strength will be noted immediately after a drug name and is commonly expressed in terms of milligrams (mg) or micrograms (mcg) for oral tablets or capsules, milligrams/milliliter (mg/mL) for liquid preparations, and grams (g) for topical creams, gels, and ointments. Drugs may also be available in more than one strength. For example, tablets of the blood-thinning drug warfarin are available as 1 mg, 2 mg, 2.5 mg, 3 mg, 4 mg, 5 mg, 6 mg, 7.5 mg, and 10 mg.
The dose of a drug is the amount to be taken at any one time and is determined by a variety of patient-specific factors, such as age, weight, kidney function, and other diagnoses and drugs. In the case of warfarin, a patient may be prescribed warfarin 8 mg once daily. In that case, the dose is 8 mg, but two warfarin tablets of the 4 mg strength are needed to achieve the target dose. In some cases, the total daily or weekly dose is provided (e.g., “Take alendronate 70 mg by mouth once weekly”) or the dose may be less, well, prescriptive (e.g., “Apply a small amount of cream twice a day to the affected arm”).
The indication of legend is the reason for which a prescription or OTC drug is prescribed or recommended, in keeping with the drug’s FDA approval (or legend). The dosage for a drug may differ by indication. For example, the starting dose of sertraline (Zoloft) for post-traumatic stress disorder is 25 mg once daily, but for major depressive disorder it is 50 mg once daily. Finally, if a drug is prescribed for a reason other than its indicated legend, then that drug is considered to be used “off-label”.
A drug’s dosage form is another term for its physical form. Drugs come in all shapes (e.g., tablets, capsules, solutions, creams, and patches) and sizes (e.g., 25 mcg, 500 mg, and 1 g). One important dosage form to counsel on is the suspension, as it needs to be shaken in order to evenly disperse the suspended particles and deliver a uniform dose to the patient.
A drug’s size, shape, color, and dosage form make up its physical appearance. The physical appearance of a drug may differ between manufacturers, and especially between brand and generic drug manufacturers; as such, if a patient reports that the color of their tablet has changed from last month to this month, then it may not mean that the wrong drug was given. In the case of warfarin, however, each of the nine tablet strengths is a different color, which helps patients (and healthcare professionals) identify that they are taking the correct one.
Common administration routes include inhalation, oral, nasal, rectal, vaginal, topical, and transdermal. It is of the utmost importance to accurately identify the intended way for a drug to be given. In the case that a patient would take a capsule by mouth instead of inserting it into the rectum, drug absorption, safety, and/or efficacy may be compromised. If there is a question about the route of administration, then a call to the prescriber should be placed to clarify.
The duration of drug therapy is determined by the diagnosis and other patient-specific factors. Chronic conditions, like depression or diabetes, may require ongoing medication treatment. More acute problems, like pain or an infection, may just need to be treated for a few days or weeks. If patients take medication for less or more time than intended, it could cause problems down the road, such as uncontrolled diabetes or antibiotic resistance.
Unwanted adverse (negative) drug side effects are common and can range from mild to severe reactions. Patient counseling should include education about what side effects to look out for and what to do in the case that side effects occur.
Side effects for a given drug can often be predicted based on how a drug works; however, because side effects are not part of the intended therapeutic effects of a drug, they are considered unwanted. Common side effects may include headache, stomach upset, or dizziness; some side effects go away over time while others are expected to continue for as long as a drug is being used. Even with the same drug, side effects may also differ by dose, dosage form, and route of administration.
Severe side effects are those that negatively impact a person’s wellbeing or their disease management. Muscle pain and cramping are common side effects of -statin medications used for high cholesterol. Over time and with dose increases, the muscle pain may be unbearable and cause the patient to stop taking his or her medication. On the other hand, a patient may not feel any different on their -statin medication, but a laboratory test may show that they have developed liver dysfunction. This would be another severe side effect, though not one that makes the patient feel differently.
While a drug’s most common side effects can often be predicted, allergies are much less predictable because the body’s immune response differs significantly from person to person. Allergic reactions account for just 10% of all drug side effects; however, allergic reactions can be life-threatening. Anaphylaxis is the most serious allergic reaction and can result in hives, swelling of the face or throat, wheezing, and even death; antibiotics are the most common cause of anaphylactic reactions. It is important to note that some patients are allergic to inactive (non-drug) ingredients, such as gluten or dye; drug compounding allows for medications to be made to suit specific patient needs such as these.
“Therapeutic contraindication” is another term for a case in which two drugs should not be used together. Generally speaking, the potential risks outweigh the potential benefits. A “relative contraindication” suggests that caution should be used when combining two drugs, whereas two drugs that are identified as an “absolute contraindication” should never be used together because of the potential for a life-threatening situation to occur. Drugs may also be contraindicated in certain conditions like pregnancy or because of age.